1. Field of the Invention
This invention relates to the recovery of phosphate from waste and more particularly to the recovery of orthophosphate used to reduce bacterial contamination of raw meat during slaughter or evisceration.
Trialkali orthophosphate, used to reduce salmonella and other bacterial contamination during slaughter of animals is either mixed, with or without concentration, with other waste products such as offal and rendered or processed with heat to form an animal feed or other by-products. The orthophosphate is mixed with a stoichiometric excess of an alkaline earth salt and the precipitate slurry concentrated or not, then added to the rendering process. Alternatively the precipitate is filtered or otherwise concentrated as by centrifuge or the like, dried, sterilized and sold as an animal food supplement.
In either method, the nutritional value of the phosphate is recovered preventing contamination of the environment and yielding an economic source of phosphate for animals. Preferable, aqueous trialkali metal orthophosphate waste is reacted with an alkaline earth metal salt and the resulting alkaline earth phosphate precipitate recovered by either admixing with animal feed during processing or by recovery of the precipitate by filtration, centrifugation or the like. The precipitated phosphate, such as calcium phosphate is mixed with animal feed such as offal or sold separately to produce a source of inexpensive calcium and phosphate.
Alternatively the orthophosphate may be thickened with gum prior to addition to offal or may be solidified by addition of excessive alkaline earth metal oxide or hydroxide.
2. Description of the Prior Art
It is known to treat animal slaughter waste by rendering to recover economic animal feed and oils. See, for example, U.S. Pat. No. 3,961,096, to Emanuel which treats poultry waste and recovers solids for use as stock feed and a uric acid precipitate. See, U.S. Pat. No. 3,412,671, which discloses dry rendering of organic material such as offal and the like to recover a solid material and oil.
The reaction of a calcium salt and phosphate is also broadly known as well as means for recovering phosphate from waste ore streams. For example, U.S. Pat. No. 4,383,847 teaches recovery of phosphorous for use in fertilizers. Such recovered phosphate may be used as animal feed as disclosed in U.S. Pat. No. 253,330,619 which recovers alkali metal phosphate salts from an aqueous leach solution of soda roast ferrophosphorous with acids. The patent teaches reaction of the recovered alkali metal phosphate with an alkaline metal oxide or hydroxide in order to recover the alkali metal hydroxide for recycling to the soda roast operation and recover the alkaline earth metal phosphates for recycling to an electric furnace for further processing with elemental phosphorous and/or recovery of calcium phosphates as an animal feed supplement.
U.S. Pat. No. 2,940,938 teaches making colloidal suspensions of certain phosphates for use as detergency builders.